The present invention relates generally to high-power lasers. More specifically, the present invention relates to a high-power, single-mode laser having both a gain medium and a single-mode filter within the resonance cavity.
Known lasers that produce relatively high output powers often each have a gain medium that produces multiple transverse modes. Such lasers each can produce an output beam having a particular spatial distribution based on the particular multiple transverse modes generated by the gain medium. In other words, different transverse modes produced by a laser have different associated spatial distributions.
These different spatial distributions can be used to select a particular transverse mode or modes (and filter out the remaining transverse mode(s)). For example, it is often desirable to modify a laser (having a gain medium that produces multiple modes) so that its output beam has only a single transverse mode, the fundamental mode.
The fundamental mode can be selected, for example, by placing a spatial aperture within the resonance cavity of the laser to filter certain undesired transverse modes. In addition, the mirrors of the resonance cavity can be designed to favor a particular transverse mode. Alternatively, a particular transverse mode can be selected (and the remaining modes filtered out to varying degrees) by taking advantage of the differences in wavelengths of the multiple transverse modes. For example, a prism located within the resonance cavity can refract the light produced by the gain medium so that only certain transverse modes are reflected by the resonance cavity mirrors.
These different approaches for selecting a particular transverse mode, however, do not work well on lasers producing relatively high output power. Specifically, a gain medium that produces relatively high output powers typically produces a large beam spot (i.e., wide beam cross section) having a relatively high power density. Consequently, it can be difficult to perform mode filtering using techniques that require a narrow beam cross section.
Disadvantages of the known lasers can be alleviated by embodiments of the present invention. In one embodiment, a single-transverse-mode laser has a gain medium and a single-transverse-mode fiber disposed within a resonance cavity. The single-transverse-mode fiber has a filter portion and a partial reflection portion. The filter portion of the single-transverse-mode fiber is coupled to the gain medium and disposed within the resonance cavity. The partial reflection portion of the single-transverse-mode fiber defines one end of the resonance cavity. The gain medium has a double-tapered structure.